Mohamed Ibrahim Moalimuu appeared to be the sole target in the attack near his residence by a busy intersection in the capital, Mogadishu.
The al-Qaida-linked al-Shabab extremist group that controls parts of Somalia often carries out bombings at high-profile locations in the capital.
Somalia President Mohamed Farmajo said Monday he has suspended Prime Minister Mohamed Roble over corruption allegations.
Amin ambulance service said at least 15 wounded people have been rushed to a hospital.
Fawzia Yusuf H. Adam's presidential campaign has been relatively low-profile because of insecurity caused by terrorist groups and the COVID-19 pandemic.
Dr. Mohamed Nur at the Medina Hospital told reporters that the toll reflected only the dead and wounded who were taken to the facility in Mogadishu where he works.
The al-Qaida-linked al-Shabab extremist group claimed responsibility. The group often targets security forces in Mogadishu.